Turkey on Sunday dismissed U.S. threats of sanctions if it went ahead with a Russian missile purchase, saying it would not renege on a pledge to Moscow.
Washington has warned its NATO ally for months that Ankara's adoption of Russian S-400 missile technology alongside US F-35 fighters would pose a threat to the jets and endanger Western defense.
The U.S. has said it will halt a joint F-35 program with Turkey if it acquires the Russian missile defense system. A U.S. law furthermore provides for sanctions on any country concluding arms deals with Russian companies.
"The U.S. threats of sanctions shows that they don't know Turkey," Vice President Fuat Oktay told Kanal 7 television.
"The decision on the S-400 has been taken. Once a pact has been signed, one's word given, Turkey respects it," he said.
The S-400 purchase is one dispute fueling tensions between two nations also at odds over US support for Syrian Kurdish militias which Ankara brands as terrorists and Turkish backing for US foe Venezuela.
Ankara said the first deliveries of the S-400 are scheduled for June or July.
Last month, after repeated warnings, the United States said Turkey's decision to buy the S-400 system was incompatible with it remaining part of the emblematic F-35 jet program.
Turkey had planned to buy 100 F-35A fighter jets, with pilots already training in the United States.
Washington has placed a freeze on the joint manufacturing operations with Turkey, and suggested Ankara might be able to obtain a U.S. missile defense system if it forgoes the one on offer from Moscow.